The present invention concerns an apparatus for severing a fibre layer composed of mutually slideable staple fibres, with two driven pairs of rolls, which form two nip lines for the fibre layer guided therebetween.
The term fibre layer as used in the context of the present invention and this disclosure is understood to describe any fibre array extending in longitudinal direction, independently of the form of its cross-section, i.e. fibre arrays of circular or centrally symmetrical cross-sections (such as e.g. the drawframe slivers in staple fibre spinning) as well as of elongated cross-sections (such as e.g. the fibre layer in a lap-forming machine or the web of a card in staple fibre spinning), in which the fibres are arranged in any shape (e.g. as longitudinally extended individualized fibres or flocks) and cohere substantially only owing to the interfibre adhesion forces.
Severing a fibre layer is known to be effected by guiding the fiber layer through the nip lines of two consecutive driven pairs of rolls, the surface speeds of which (which for continuous transport of the fibre layer without a draft are chosen the same, or, if a draft is to be effected between the nip lines, are chosen in a ratio corresponding to the draft ratio desired) can be changed relative to each other to such a degree, that the fibre layer is torn apart and thus is severed. Such severing methods are described, e.g. in German Pat. No. 910 754, in which it is shown already also, in which manner, according to first solutions the severing is effected by a sudden acceleration of the pair of delivery rolls, arranged, as seen in the direction of fibre transport, as the subsequent pair of rolls, as it can be effected, according to a further solution, by suddenly slowing down the pair of input rolls arranged as the first pair of rolls, as seen in the direction of fibre transport. These two solutions operate under application of at least one clutch, by means of which the drive of the pair of delivery rolls can be coupled with a faster rotating shaft for acceleration, or, respectively, the drive of the pair of input rolls can be de-clutched, and thus, the pair of input rolls can be brought to standstill.
These solutions show the disadvantage that a complicated drive system for the pairs of rolls, with at least one clutch, is required, which renders the device expensive and requires a great deal of maintenance work.